Quaternary Ammonium Surfactant Alkyl Chain Length-Directed Evolution of AuCu–Cu Janus Nanoparticles into AuCuAg Heterostructures for Plasmonic Catalysis

Abstract Engineering the composition and structure of multimetallic nanostructures provides a versatile means to tailor their plasmonic and catalytic properties. Herein, a seeded-growth approach combined with surfactant-directed galvanic replacement is used to prepare AuCu–Cu and AuCuAg nanostructures with well-defined compositions and architectures. Spherical Au seeds were first grown into trisoctahedral Au nanoparticles and then transformed into AuCu–Cu Janus nanoparticles (JNPs). Galvanic replacement with Ag in the presence of CTAC or OTAC yielded AuCuAg nanoparticles (NPs) or AuCuAg hybrid nanoparticles (HNPs), showing that the alkyl chain length of the quaternary ammonium surfactant directs the structural evolution during Ag incorporation. Using NaBH4-mediated reduction of 4-nitrophenol as a model reaction, all catalysts exhibited enhanced rate constants under light irradiation. AuCuAg HNPs give the highest absolute light-driven rate (0.145 min–1), while AuCuAg NPs give the largest light/dark enhancement factor (about 8.2). Finite element method simulations show that the dominant absorption shifts from ∼735 to ∼640 and ∼855 nm for the three structures, with the electric field localized at heterointerfaces and geometric boundaries. This work clarifies how surfactant chain length governs the structural evolution of multimetallic heterostructures and provides a mechanistic framework for interpreting plasmonic enhancement in such systems.